branch,
No, CTs won't work with a DC system (unless the motor are PWM). I, somehow, overlooked that little tidbit of info.
You could, however, depending on the current draw of a motor, use a very low value (typically, 1Ω), high wattage resistor, in series with one lead feeding the motor and monitor the voltage developed across the resistor. This would be identical to the CT systems used with AC.
You might consider taking this data (and this would not be simple; Mikebits is absolutely correct) and using it to "page" (text, tweet??) you when a system has failed.